The present invention is described below with respect to a liquid crystal shutter and driver electronics. It will be appreciated, though, that features of the invention may be utilized with shutters formed of materials other than liquid crystal, with different types of electronic circuits and also with devices other than shutters. A shutter, as is used herein, refers to a device for controlling intensity of electromagnetic energy or electromagnetic radiation that is being transmitted through the shutter. In the preferred embodiment described in detail below, such electromagnetic energy is in the form of light and more preferably is in the form of light (i.e., electromagnetic energy) that is in the visible spectrum as well as in the various infrared spectra and ultraviolet spectra, all collectively referred to as light below. Such control may be by way of graduated or analog control of intensity of transmitted light preferably without detrimentally affecting the image characteristics of such light. Such control also may be digital, i.e., on, off, and specific intermediate levels of transmission or intensity, etc.
According to the best mode, the shutter and the circuit of the invention are used as an automatically darkening welding filter to protect the eyes of a welder during welding. It will be appreciated that the invention may be used for other signal detection purposes and the like, too.
Exemplary liquid crystal shutters with which the driving circuit of the invention may be utilized are disclosed in U.S. Pat. Nos. 4,385,806, 4,436,376, 4,540,243, and Re. 32,521 or in U.S. patent application Ser. No. 07/674,850 for "Liquid Crystal Lens Driver Electronics For Eye Protection and High Speed Shuttering". An example of such shutters includes a pair of linear (plane) polarizers, one being used as an input polarizer and the other as an output analyzer, and a variable liquid crystal optical retarder between the two polarizers. By changing the electric field applied to liquid crystal in the retarder, the plane of polarization (or relationships of the axes of elliptically polarized light) of the light transmitted through the retarder can be changed; and the intensity of light transmitted through the analyzer will be a function of the polarization direction (characteristics) of the light transmitted through the retarder.
A shutter system which may employ such an exemplary liquid crystal shutter is disclosed in copending, commonly owned U.S. patent application Ser. No. 07/653,661 filed Feb. 8, 1991, for "Eye Protection System For Welding Helmets And The Like". The present invention is useful to provide electrical power and to operate such a shutter system and the shutters mentioned in the preceding paragraph. Exemplary shutters which may be used in connection with this are sold by OSD Envizion Company of Menlo Park, Calif.
The disclosures of the above patents and patent applications are incorporated in their entireties by this express reference thereto. The exemplary shutter and driving circuits of such patents and applications and of this application may be used in a variety of embodiments and applications. One example is as a lens or shutter for a welding helmet.
The terms "lens", "welding lens", and "welding filter" are used herein synonymously with "shutter" and as used herein means a device through which an image may be viewed usually without necessarily having any significant focusing or optical refraction characteristics. The lens or shutter is adjustable to control light, i.e., to increase or to decrease the amount of the incident light which is transmitted through the shutter. When welding is not occurring, the shutter may be substantially optically clear or transmissive or at least minimizes its attenuation of light. When welding is occurring, the shutter may be dark or closed to minimize the amount of light transmitted therethrough in order to protect the eyes of the person performing the welding. In both cases, though, the image characteristics of the light remain intact. A photosensitive device may be used to sense the intensity of light impinging in the area of the shutter so as to provide an input to the driving circuit for the shutter in order to control opening and closing thereof.
The present invention is especially useful for eye protection wherein detection of a bright light source and high speed protective shuttering are desired. Exemplary uses are in welding helmets, spectacles, goggles, and the like, as well as safety goggles for nuclear flash protection, for protection from hazards experienced by electric utility workers and for workers at furnace and electrical plant areas and at other places where bright light that could present a risk of injury may occur. The present invention is useful in other non-eye protection fields such as where high speed detection and shuttering of light will provide for more comfortable operation of certain equipment such as high speed detection of headlights approaching from the rear for automatically dimming rear view mirrors in automobiles. The present invention is also useful for protection and tuning of optical measurement equipment in a variety of laboratory, test and production environments.
The difference in light intensity between indoor ambient light and welding light usually is larger than the difference in light intensity between bright sunlight ambient and welding light, and prior sensor devices and circuits were not able automatically and conveniently to adjust for such different ambient conditions. U.S. patent application Ser. No. 07/674,850 discloses a photosensitive sensor circuit and driving circuit for use in automated welding lens systems with a sensor operational range that functions well in both indoor environments and outdoor environments, that automatically adjusts to the relatively gradual changes in ambient light compared to rapid changes due to initiation of a welding arc, flame, etc, and that operates relatively rapidly in order rapidly to operate the shutter driven thereby. Sensor devices prior to the invention disclosed in such patent application did not adjust automatically to accommodate the change in ambient conditions, for example, when the door to a room is opened to allow bright sunlight to enter the room, and, therefore, such prior devices possibly falsely might trigger a detection of welding or impede proper sensitivity to welding in such a case. In the sensor circuit portion of the drive circuit of Ser. No. 07/674,850 a manual adjustment was provided to accommodate particular ambient light conditions and also to accommodate the pulsed type or continuous type of light emitted during welding, e.g., during MIG welding or TIG welding, respectively.
It is desirable to have the full functions described in U.S. patent application Ser. No. 07/674,850, including the ability to detect the presence of a bright light source regardless of the light source characteristics (AC, i.e., pulsating or MIG welding, or DC, i.e., continuous or TIG welding, type light waves) and regardless of the ambient light level and source. It is further desirable to have the circuit automatically adjust to the ambient environment and detect all types of bright light hazards with no adjustments required by the operator whatsoever.